This application claims priority of International application number PCT/JP01/11156, filed Dec. 19, 2001, which in turn claims priority of Japanese application number 2000-387581, filed Dec. 20, 2000,.
1. Technical Field of the Invention
The present invention relates to a method for detecting a stationary object located above a road, in particular, an overhead structure such as a bridge over a road, by using radar detection in combination with camera image processing.
2. Backgroud Art
A scanning radar scans a radar beam by moving the beam from left to right or from right to left at very small step angles within a predetermined time. At each step angle, the radar beam is projected from the radar-equipped vehicle toward a vehicle traveling in front, and the reflected wave from the vehicle in front is received and processed to detect the presence of the vehicle in front and compute the distance and relative velocity with respect to that vehicle.
In the case of a radar, as the beam is usually scanned in lateral directions as described above, it is difficult to obtain accurate information on height. As a result, when an overhead structure such as a bridge over the road ahead or a structure such as a road sign located on the roadside in front is detected, it may not be possible to distinctly identify whether the detected object is a stationary structure located above the road or on the roadside in front or a vehicle traveling in front.
It is an object of the present invention to provide a method for detecting a stationary object located above a road, which, when an object is detected in the path in front, can identify whether the detected object is a vehicle traveling in front or a structure, such as a bridge or road sign, located above the road or on the roadside in front.
According to the method of the present invention, the method uses a camera and a radar system, and when it is determined that the target captured by the camera is the same target that has been captured by the radar, and when it is determined from an image captured by the camera that the target is at a height higher than the horison level, the method determines that the target is a stationary object located above the road.
Further, according to the method of the present invention, when it is determined that the distance to the target captured by the camera or the radar is decreasing, and that a reception level from the target captured by the radar is also decreasing, the method determines that the target is a stationary object located above the road.
According to the method of the present invention, when it is determined that the target captured by the camera is the same target that has been captured by the radar, and when it is determined from the image captured by the camera that the height of the target, for example, the height above the road in the case of a road sign or the like, is equal to or higher than a predetermined value, the method determines that the target is a stationary object located above the road.
According to the method of the present invention, the method uses a camera system, and when it is determined that the length of a vertical edge or horizontal edge of the target captured by the camera is increasing with time, the method determines that the target is a stationary object located above the road.
The camera system comprises a multiocular camera or a monocular camera. The method of the present invention determines that the two targets are the same target when the difference between the distance Rg to the target captured by the camera and the distance Rr to the target captured by the radar and the difference between an angle xcex8g of the target captured by the camera and an angle xcex8r of the target captured by the radar are within a predetermined range.
When it is determined that the target is a stationary object located above the road, data obtained from the target is deleted from data concerning a vehicle traveling in front.
According to the method of the present invention, since information about the height of the target, which cannot be obtained by the radar system alone, is obtained from an image captured by the camera system, it can be determined in a simple manner whether the detected target is a stationary object located above the road.
Further, according to the method of the present invention, whether the detected target is a stationary object located above the road can also be determined in a simple manner by detecting a variation in the reception level obtained by the radar system.
Furthermore, according to the method of the present invention, whether the detected target is a stationary object located above the road can also be determined in a simple manner from edge information which is image information obtained from the camera system.
When the above methods are combined, it becomes possible to determined in a simple and more reliable manner whether the detected target is a stationary object located above the road.